1. Field of the Invention
This invention relates to apparatus for synchronizing the flash lighting with the camera shutter.
2. Description of the Prior Art
As the conventional example of the strobe synchronizing method, there has been known Japanese Laid-Open Patent Application No. SHO 58-42033 in which, as shown in FIG. 1, a range finder 51 with a counter produces an output in digital form which is then factored into the guide number of a strobe 58 by a decoder 52 to determine the required value of aperture. This value is set in a DOWN counter 53. The sensitivity of the used film is set in an input device 54. Counting down the output of the input device 54, the DOWN counter 53 produces an output as a reference level for a comparator 57. As the shutter is opening, an aperture detector 56 produces a corresponding number of pulses to the actual size of aperture opening of the shutter which are applied to an UP counter 55. When the output of the UP counter 55 exceeds the output of the DOWN counter 53, a comparator 57 produces an actuating signal for firing the strobe 58. Thus, a proper flash exposure is made. In this method, however, there is need to use two counters, and, moreover, one of them is the DOWN counter. Therefore, the electrical circuit is increased in scale and becomes complicated in structure. This calls for an increase in the production cost. Another disadvantage is that the manufacturing techniques and the maintenance becomes very difficult.
In the art of lens shutter cameras, the photographic lenses have generally as short focal lengths as 28 to 40 mm. To take an image of a subject of principal photographic interest in large proportion, therefore, the camera has to approach so much near to the subject. For this reason, a camera having two focal lengths, or the standard and telephoto settings has come into the market. As a result, though the aforementioned drawback has been removed, the conventional strobe flash-camera shutter synchronizing apparatus shown in FIG. 1 can no longer be employed in such focal length changeable camera, because the output of the aperture detector does not correspond to one and the same aperture value when the focal length is changed over between two different values, for, as the diameter of the entrance pupil of the photographic lens remains constant, the change of the focal length results in a change of the aperture value at the full opening.
As the technique of speeding up the sensitivity of film advances, the amount of flash light the ordinary strobe usually emits becomes so large that with the near subject, even when the aperture opening is of the smallest size, an over-exposure results. To avoid this, the amount of flash light of the strobe may be made variable stepwise in accordance with the film speed or the object distance. In this case, however, it also follows that the aforementioned conventional synchronizing method can no longer be used. Further, there is another photographic situation where the photographer desires to alter the flash exposure value according to his experience and insight, for example, when a special filter is used with the result of reduction of the intensity of flash light, or when the flash illumination is brought into good balance with the ambient light. In these cases, too, the aforementioned conventional synchronizing method becomes out of use, because the value of the correction factor for use in computing the aperture value for flash exposure must be changed.